This invention relates generally to a mechanical pressing machine, and more particularly to a mechanical pressing machine provided with a dynamic balancing device for balancing an unbalanced inertia force produced in a reciprocally-moving mechanism utilizing a crankshaft.
Generally, in a mechanical press utilizing a crankshaft, a slider is connected to an eccentric crank portion of the crankshaft through a connecting rod, thereby converting a rotational motion of the crankshaft into a reciprocal motion of the slider. When the operation of such a pressing machine utilizing the crankshaft is started, vibrations, resulting from an unbalanced inertia force due to the reciprocal movement of the slider, develop to produce noises and to cause a positional error. To avoid this, usually, a dynamic balancing device has been used.
In a conventional dynamic balancing device, an unbalanced inertia force of a reciprocating slider is canceled by a balance weight which is equivalent in weight to the slider, is mounted on a crankshaft, and is disposed 180.degree. out of phase. With this construction, the unbalanced inertia force in the whole of the press is canceled by the balance weight, and vibrations of the press itself (except for the slider and the moving parts) are reduced, and the press can be operated at high speed.
In the above conventional pressing machine, however, although the unbalanced inertia force of the slider is canceled by the balance weight, the inertia force exerted on the slider during the reciprocal movement acts on both of the slider and the balance weight to increase the dynamic load, since the slider and the balance weight are separately supported on a frame. This increase of the inertia force causes a flexure in accordance with the spring constant of the crankshaft and the slider, and has adversely affected a dynamic precision such as a lower dead center precision and a coining precision.